There is a need for improved tire recycling operations both to address the need to dispose of used tires in an environmentally sound manner and to satisfy an estimated $68 billion per year demand in the U.S. for rubber. This market increases at a stable rate of approximately 6% per year.
In the U.S. alone there is a need to dispose of over $300 million in used tires annually. Approximately 12% of tire refuse currently ends up in landfills.
Currently, 52% of used tire refuse in the U.S. is disposed of by creating tire derived fuel (TDF). However, a crisis is emerging in the recycling industry because TDF is a controversial “dirty” type of fuel. TDF fuel fails to meet EPA emission standards. It is expected that this disposal/recycling method will be foreclosed and other methods for recycling and tire disposal will be desperately needed as TDF fuel no longer remains a recycling and disposal option. Only about 17% of refuse tire rubber is presently recovered and re-used to produce actual rubber products. The economics of recycling rubber products are tenuous, because the present art relies on using a cumbersome multi-step process that must be performed at multiple locations. The end usable product is referred to as “crumb rubber.”
As consumer demand for products containing ground or crumb rubber is increasing, the desirability of diverting more tire refuse to crumb rubber production is apparent.
A recycling crisis coupled with demand for a recycle product create a unique, historic economic opportunity which present rubber recycling and crumb rubber processing technologies cannot address. Industries will pay a premium price both for rubber disposal options and for high quality crumb rubber. It is desirable to have a technology positioned to take advantage of these converging economic trends.
Current rubber recovery processes are highly inefficient and marginally profitable, under the best of circumstances. Tire shredding and methods of recovering rubber, steel and fiber from used tires are processes known in the art. Current processes generally recover approximately 78-92 percent of the total rubber material in a tire, but the quality of rubber is substandard for many commercial uses. The end-product rubber contains significant metal contaminant and iron oxide contaminants. These contaminants prevent the rubber from meeting the requirements for end-uses for any high-end products.
Water-jet processes for reclaiming rubber from used tires are known in the art; however, these methods require some shredding. These methods are inefficient and lead to contamination, which lowers the value of the recovered rubber.
The American Society for Testing and Materials (ASTM), which is an international organization charged with developing standards for rubber and other materials, promulgates standards for rubber which dictate the uses for recovered rubber. ASTM standards establish the level of contaminants and other materials.
Crumb rubber, or recycled rubber that has been reduced to particles, is the most valuable type of recycled rubber. The size of the particles is referred to as “mesh size.”
Tyler mesh size is the number of openings per (linear) inch of mesh. To calculate the size of the openings in a mesh the thickness of the wires making up the mesh material must be taken into account. In practice, mesh openings are determined referring to a chart like the one below which uses a scale known as the Tyler mesh scale:
Sieve sizeTylerUS(mm)BSS(approx)(approx)4.75—443.355662.816772.387882.0089101.681010121.401212141.201414161.001616180.8531820200.7102224250.5992528300.5003032350.4223635400.3544442450.2975248500.2516060600.2117265700.1788580800.1521001001000.1251201151200.1041501501400.0891701701700.0752002002000.0662402502300.0533002702700.0443503253250.037440400400
In addition to standard U.S. and Tyler mesh sizes, commercial sieves in the U.S. can also utilize three other standards.
A problem known in the art is that tire recycling operations are inherently costly because they involve a number of sequential size reduction steps to convert used tire rubber to “crumb rubber” which is usable for rubber products.
Generally, the tire recycling process is a costly, low-yield, high cost process involving one or more of the following steps using multiple machines at multiple locations using conveyors and “air movement” systems:                Primary shredding process—Cutting/shredding tires into sections using a primary shredding process that reduces the space required for transporting the tires for further processing (i.e., air space within the tire structure). Generally, this will produce remnants of rubber, steel and fiber that vary in size. This process is generally performed by shredding machines, rapsers and other machines for reducing the size of tires known in the art.        Secondary shredding process—Further reduces larger sections of rubber into chips (e.g., 3 inches or less). During this process, rubber, steel and fiber are co-mingled, producing a quantity of mixed fragments of each. This process is generally performed by a “secondary shredder” known in the art.        Tertiary shredding process—This process is a further size reduction process which is generally used to create even smaller chips (depending upon the end use for the product). Currently, tires must be reduced in size in some manner because current machinery known in the art is not adapted to remove rubber directly from tires.        Grinding and hammer milling process—Reducing the chips into rubber particles with varying mesh size (which is a measurement of size reduction based on holes per square inch).        Removing the steel for sale to those respective markets—This process often uses multiple magnets during a sifting process.        Removing the fiber for sale to those respective markets—The machine known in the art that performs this function is generally referred to as an air “classifier” or “air gravity separation chamber.”        
Generally, the price for which recovered rubber and steel can be sold depends upon the level of contaminants in the product. It is therefore desirable to reduce the levels of contaminants in the product.
Rubber which meets the (ASTM) standards for a wider variety of products (e.g., such as off-road tires, automotive, consumer products) can be sold at a higher price. Specific materials standards apply to various types of products. Rubber that does not meet the standard for high-quality uses is sold for less. For example, rubber which meets higher ASTM standards may sell for as much as twelve times the cost of lower quality rubber (e.g., asphalt, fuel grade or aggregate quality rubber).
Generally, using current processes, the higher the rubber recovery rate the more metal contaminants the rubber will have. For example, a process which scrapes rubber and avoids contact with the metal tire treads will be reasonably free of metal contaminants, but will have a relatively low recovery rate. A more efficient tire stripping method will recover a greater percentage of rubber, but the rubber will include more iron oxide and metal contaminants.
A similar problem exists with regard to steel recovered in the process. Generally, steel recycling (“smelting”) requires recovered steel which has less than 5% rubber (by volume) adhered to the steel. With current tire recycling processes, the higher recovery rates usually result in increased levels of rubber contaminants.
It is desirable to have a single integrated machine and/or system to reduce the number of steps and processes necessary to reduce rubber to crumb rubber.
It is further desirable to increase the quantity of rubber and steel that can be recovered from each used tire.
It is further desirable to increase quality of rubber and steel recovered from used tires consistent with ASTM standards because recovered material has an increased value and can be used for a wider range of purposes.
It is further desirable to extend the mechanical life of equipment currently used to recover rubber, steel and fiber from used tires.
It is further desirable to integrate the de-vulcanization and re-vulcanization processes with tire recycling and recovery processes.
It is further desirable to reduce the operating costs of tire recycling operations.